The addition of milk protein preparations is often used in the production of fermented dairy products for the purpose of increasing the content of dry matter in milk. And then prebiotics are applied in order to improve the growth of probiotic bacteria in fermented milk beverages and thereby to maintain the functionality thereof at adequate levels. The objective of this study was to determine the effect of selected prebiotics (oligofructose, inulin, and resistant starch) and whey protein isolate (WPI) on rheological properties of bio-yoghurt produced with the use of inoculum containing probiotic bacteria. Compared to the supplementation with only WPI, the application of mixtures containing WPI and selected prebiotics caused the hardness of bio-yoghurts to increase. As for the mixtures of resistant starch (RS) (1.2 N) and oligofructose (1.1 N), the highest hardness of the yoghurt curd was achieved at a 1.5 % concentration rate of WPI. The addition of 1 % of WPI and 1 % of RS caused the acid curd formation process to expedite; the acid curd formation process started already 98 min after fermentation compared to 135 min in the case of the control bioyoghurt. (original abstract)